1. Field of the Invention
The present invention relates to image forming apparatuses, and in particular to digital image forming apparatuses such as a copier, a printer, and a facsimile that electrophotographically form images.
2. Description of the Related Art
There are mainly two methods of reading an original with an image reading device included in an apparatus such as a digital copier, scanner, or facsimile: an optical-system-moving method in which an image is read by moving an optical system while the position of the original, which is placed on a glass table, is fixed; and an original-moving method in which an image is read by conveying the original with an original feeder (automatic document feeder: ADF) while the position of an optical system is fixed.
The original-moving method has a problem in that foreign substances, or dust particles, adhered to a platen glass may be imaged as lines extending in a sub-scanning direction, or a direction in which the original is conveyed. To solve this problem, Japanese Patent Laid-Open No. 10-56542 discloses a first exemplary technique in which a reference member having a certain color is provided in such a manner as to face a platen glass, along which an original is conveyed, and the presence of any dust particles is checked in accordance with the result of reading the reference member.
In the first exemplary technique, stationary dust particles adhered to the platen glass can be detected, but stray dust particles following the movement of the original cannot be detected. To solve this, Japanese Patent Laid-Open No. 2006-173933 discloses a second exemplary technique of detecting such stray dust particles.
While the first and second exemplary techniques are each a method of detecting dust particles, Japanese Patent Laid-Open No. 2002-84392 discloses a third exemplary technique in which a report showing the positions of detected dust particles by providing marks thereat is printed.
All of the foregoing exemplary techniques, however, have respective problems described below and have been desired to be further improved.
The first and second exemplary techniques have the following problem. Although lines formed by stationary dust particles and stray dust particles following the movement of the original can be detected, it is not easy for a user to locate the detected dust particles on the original. Particularly in the second exemplary technique, although an independent line extending in the sub-scanning direction and including less than a certain number of pixels is recognized as a line formed by a dust particle, such a line cannot be distinguished from an actual printed pattern.
The third exemplary technique, in which a report showing the positions of dust particles by providing marks thereat is output, has the following problem. If, for example, such a report is output while a large number of images are formed, the report is mixed into the resulting printed matter.